Polyethylene terephthalate homopolymer (PET) has succeeded as a replacement for glass in many applications. The success of PET as a glass replacement is attributable to a large extent to the fact that it is very light weight and will not normally break and shatter on impact. PET also offers good carbon dioxide and oxygen barrier resistance and can accordingly be utilized in carbonated beverage bottles. Bottles, jars and cans which are made from PET are currently being utilized as containers for a wide variety of food products and beverages. However, PET containers are not suitable for some food products which must be packed utilizing hot-fill techniques. This is because containers made from PET can become thermally unstable above the glass transition temperature of the PET (about 74.degree. C.).
Heat-setting techniques can be utilized to enhance the thermal stability of PET containers. By utilizing heat-setting techniques, the service temperature of PET articles can be increased to about 80.degree. C. This allows for such heat-set PET containers to be utilized in certain hot-fill applications which would not otherwise be possible. For instance, heat-set PET containers can be hot-filled with fruit juice which would not be possible if the container was not heat-set. Even though heat-setting is effective for increasing the service temperature of PET containers, the cost associated with the heat-setting procedure is very substantial.